1. Field of the Invention
The present invention relates to a blood collection device for receiving a sample of whole blood, and more particularly, concerns such a device wherein the blood is to be centrifuged into lighter and heavier phases of specific gravity. The present invention further contemplates a separator assembly for use in a blood collection device for providing a barrier between lighter and heavier phases of blood separated by centrifugation.
2. Description of the Prior Art
In the laboratory analysis of blood collected from a patient, the different constituent phases of blood require separate analysis. Blood plasma is separated from blood cells by a standard centrifuging procedure which readily accomplishes this separation since the specific gravity of the cellular phase of blood is heavier than the plasma phase of blood. In a similar fashion, whole blood is often separated into a clotted phase and a serum phase once again by centrifuging procedures and reliance upon the differences in the specific gravities of these two phases of blood. Since the whole blood is normally collected in a test tube-type of blood collection container which is subsequently centrifuged, separation of the phases occurs in the same vessel. Thereafter, removal of the separated phases from the test tube must be accomplished cleanly so that there is no subsequent intermixing of the separated phases. Various decanting procedures, both by pouring and by manual filtration devices, have been employed in the past to collect each of the separated phases following centrifugation. These procedures must, however, be done carefully and quickly so that only one phase is collected. On the other hand, these procedures normally are done immediately after the centrifuging operation because transport to another laboratory area would cause subsequent intermixing and therefore compromise the purity of the separated phases. Thus, transport of the vessel containing separated phases after centrifugation and a longer time period after centrifugation to collect one or both separated phases are features which have been sought.
Early efforts to provide a barrier or sealant between the separated phases of whole blood are described in U.S. Pat. Nos. 3,780,935 and 3,852,194. In U.S. Pat. No. 3,780,935, the sealant is introduced after the whole blood has been collected which compromises the desirable features of a closed system. In U.S. Pat. No. 3,852,194, the sealant material is initially placed at the bottom of the blood collection container, but has a tendency to move from its initial location near the closed end of the tube toward the eventual fluid-phase interface. This movement was described as undesirable in U.S. Pat. No. 3,920,549 wherein an improvement was described. This improvement included an energizer member for maintaining the gel material in a position adjacent the container bottom and then relying upon the energizer member to control the flow of the gel material due to the forces generated against the energizer member during centrifugation.
In U.S. Pat. No. 3,957,654, a sealant barrier assembly is introduced into the blood collection container after the blood has been first centrifuged and separated into its two phases. A phase partitioning device is also disclosed in U.S. Pat. No. 4,055,501 wherein the partitioning device is disposed within the collection tube before blood is collected therein. Both U.S. Pat. Nos. 3,957,654 and 4,055,501 disclose a barrier sealant within a cylindrical vessel which includes a slidable piston element. Upon centrifugation, these pistons slide to compress the volume within the cylindrical vessel thereby forcing barrier sealant material radially outwardly through holes in the vessel whereupon the barrier sealant adheres to the inside walls of the container to provide a physical separation between the phases of blood. While these patented devices describe a technique for effectuating the barrier between the lighter and heavier phases of blood, other improvements for control of the barrier material to the interface between the phases are still being sought. It is to this end that the present invention is directed.